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Abstract:
Abstract: We used functional MRI to measure neural responses
while subjects learned rules governing the arrangements of letters.
During each activation epoch, subjects were presented with 20
strings of 4 letters and were required to make a push-button
response to indicate whether the string conformed to or violated
the current rule. Trial-by-trial feedback was provided for their
responses, enabling subjects to learn the rule which was based on
the positions of a repeated letter (e.g. if first and last letter
the same, the item conforms to the rule). The rule and the 3
letters making up the 4-letter strings were constant during a given
activation epoch. However, the strings presented in the next
activation epoch were determined by a 2x2 factorial design with
presence or absence of rule change as one factor and presence or
absence of letter-set change as another factor, i.e either change
in both rule and letter-set, or change in just rule, or change in
just letter-set, or no change in either rule or letter-set. 10
subjects were scanned and the data analysed using SPM99 employing a
random effects model. Relative to the no change condition, the
introduction of a new rule evoked activation in bilateral
dorsolateral prefrontal cortex and anterior cingulate, whereas
change of letter-set activated left dorsolateral and medial
prefrontal cortex as well as left posterior fusiform.
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